<!DOCTYPE html>
<html lang="zh-CN">
<head>
    <meta charset="UTF-8">
    <title>Rounded</title>
    <style>
        .rounded {
            background-color: #00ff00;
            border-radius: 20px;
            height: 150px;
            width: 150px;
        }

        .border {
            border: 5px;
        }

        .border-property {
            border-top: 5px;
            border-right: 5px;
            border-bottom: 5px;
            border-left: 5px;
        }

        .border-radius {
            border-radius: 20px;
        }

        .border-radius-property {
            border-top-left-radius: 20px;
            border-top-right-radius: 20px;
            border-bottom-right-radius: 20px;
            border-bottom-left-radius: 20px;
        }

        .border-top-left-radius {
            border-top-left-radius: 20px 10px;
        }
    </style>
</head>
<body>
    <h1>Simple Rounded Corners</h1>
    <div class="rounded"></div>
</body>
</html>